Q5 / 160 · AP EAMCET 2020 (21 Sep Shift 2) · Chemistry

Calculate the concentration of fluorine in ppm in \(500 \mathrm{~g}\) of toothpaste containing \(0.2 \mathrm{~g}\) of fluorine.

  • A
    \(2 \times 10^2\)
  • Correct answer
    B
    \(4 \times 10^2\)
  • C
    \(4 \times 10^0\)
  • D
    \(4 \times 10^3\)

Solution

PPM or Parts Per Million is expressed as 1 milligram of substance per kilogram of parent substance. Since, mass of toothpaste \(=500 \mathrm{~g}=0.5 \mathrm{~kg}\), and mass of fluoride ion \(=0.2 \mathrm{~g}=200 \mathrm{mg}, 0.5 \mathrm{~kg}\) toothpaste contains \(200 \mathrm{mg}\) fluoride ions, \(1 \mathrm{~kg}\) toothpaste will contain \(200 \times 2=400 \mathrm{mg}\) fluoride ions. Hence, concentration of fluoride ion is \(400 \mathrm{ppm}\) or \(4 \times 10^2 \mathrm{ppm}\). Hence, option (b) is correct.

Hence, the correct answer is option: 'B'.

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